A conventional way of generating white light is conducted by exciting an optical film that includes a plurality of quantum dots. Specifically, the quantum dots are made of different materials or have different dimensions, and are excited by an incident light to emit lights that have wavelengths different from that of the incident light. The lights emitted by the quantum dots are mixed with the incident light to form white light. For example, the incident light may be a blue light emitted by a blue light emitting diode, and the lights emitted by the quantum dots may be red and green lights. The mixture of red, green and blue lights will produce white light.
The optical film may be used in a back light module of a display device, and provides the display device with wider color levels, chromaticity and color gamut, thereby achieving better viewer satisfaction.
The optical film includes a first surface through which the incident light enters, a second surface, opposite to the first surface, through which the white light exits, and aside surface connected between peripheries of the first and second surfaces. In practical use, it is found that a portion of the incident light may enter the optical film through the side surface, which may be caused by reflection, refraction or interference from an internal structure of the display device. A blue ring or blue halo is observed at a periphery of the optical film, accordingly. The blue light entering the optical film through the side surface may produce undesired excitation of the quantum dots and unwanted light mixture, which undermines image quality of the display device.